1. Field of the Invention
The present invention relates to a calibrating mechanism of an infrared analyzer.
2. Description of the Prior Art
In general, it is necessary for an infrared analyzer to carry out the zero-calibration and the span-calibration at regular intervals. Hitherto, a zero-gas is introduced into a measuring cell at the set flow rate and the zero-point is adjusted after the indication was stabilized. Subsequently, a span gas is introduced into the measuring cell at the set flow rate and the span is adjusted after the indication was stabilized. That is to say, the gas-calibrating method has been used. However, this gas-calibrating method has a problem in that an expensive gas which is to be checked with a high accuracy is required at each span-adjustment, so that the calibrating cost is increased.
Contrary to this, a mechanical calibrating method, in which the calibration is easily carried out without usually using a gas by reducing the quantity of light passing through the measuring cell by means of a light-quantity reducer such as a metallic plate, a light-quantity reducing filter or a liquid crystal element to change the quantity of light incident upon the detector, has been tried. However, according to this mechanical calibrating method, where a metallic plate is used as the light-quantity reducer, a subtle influence due to the shift of the inserting position occurs whereby an error is produced. In addition, where the light-quantity reducing filter and the liquid crystal element are used as the light-quantity reducer, the reduction of the light-quantity is changed due to staining, injury, etc. to the light-quantity reducer itself. As described above, it is difficult to hold a high accuracy when using such a mechanical calibrating method. Furthermore, the mechanical calibrating method has a disadvantage in that the trouble is apt to be produced since it includes movable parts.